1. Field of the Invention
This invention relates to microelectromechanical devices, and more particularly, to peripheral configurations of moveable electrodes relative to contact structures included in microelectromechanical devices.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Microelectromechanical devices, or devices made using microelectromechanical systems (MEMS) technology, are of interest in part because of their potential for allowing integration of high-quality devices with circuits formed using integrated circuit (IC) technology. As compared to transistor switches formed with conventional IC technology, for example, microelectromechanical contact switches may exhibit lower losses and a higher ratio of off-impedance to on-impedance. MEMS switch designs generally include a moveable electrode in the form of a beam or a plate spaced apart from a fixed electrode. The switch may include one or more contact structures dielectrically spaced above the fixed electrode and/or arranged along the same plane as the fixed electrode but isolated therefrom. While each of the contact structures may be configured to prevent the moveable electrode from contacting the fixed electrode, some of the contact structures may be “electrically active” in that they are configured to pass and receive current. In particular, electrically active contact structures may include conductive materials and are generally coupled to signal traces which are coupled to input or output signal terminals. Other contact structures, however, may be “electrically inactive” in that they are not configured to pass and receive current.
Upon actuation of the fixed electrode, the moveable electrode moves such that the moveable electrode itself or contact structures coupled to the moveable electrode make contact with the contact structures arranged adjacent to the fixed electrode. This “on state” allows current to pass through the electrically active contact structures. An “off state” corresponds to a state in which the fixed electrode is not actuated and, therefore, contact between the moveable electrode and the contact structures is not made. Due to the narrow spacing between the two electrodes of the switch, capacitive coupling between the moveable electrode and the contact structures adjacent to the fixed electrode may be high enough to cause high-frequency energy from the moveable electrode or electrically active contact structures to leak across to the opposing structure even when the switch is in the off state. The energy leakage is sometimes referred to as poor isolation and generally worsens as the capacitive coupling between the components increases.
In some embodiments, it may be advantageous to position contact structures under the moveable electrode and interior to the peripheral edge of the moveable electrode to provide structural stability to the moveable electrode during actuation. In particular, arranging contact structures under the moveable electrode between the center point and edge of the moveable electrode may serve to better hold the moveable electrode above the fixed electrode during actuation than if all contact structures were arranged under the center point and/or the edges of the moveable electrode. Signal traces coupled to contact structures which are arranged under and interior to the edges of the moveable electrode, however, are also arranged under the moveable electrode. As a consequence, the capacitive coupling of the switch may be undesirably increased, resulting in poor isolation.
It would, therefore, be desirable to develop a MEMS switch which provides low capacitive coupling as well as sufficient structural stability to prevent a moveable electrode from collapsing onto a fixed electrode. In particular, it would be beneficial to create a MEMS switch which allows contact structures to be positioned under and inbound from edges of a moveable electrode without increasing the capacitive coupling of the switch.